Chara 2?

Visible in northern skies during
Spring, Chara is Greek for "Joy." Also known as Beta Canum Venaticorum,
the star is located about 27.3 light-years from Sol. It lies in the
northwestern part (12:33:44.54+41:21:26.93, ICRS 2000.0) of
Constellation
Canes
Venatici, the Hunting Dogs -- northwest of
Cor
Caroli (Alpha2 Canum Venaticorum). The star may have a
wide companion (more below).

In late September 2003, astrobiologist
Maggie Turnbull
identified Chara as one of the best candidates for
hosting Earth-type life in a shortlist of 30 stars (screened
from the 5,000 or so stars that are estimated to be located
within 100 ly of Earth) that were presented to a group of
scientists from NASA's space-telescope project, the
Terrestrial
Planet Finder (TPF), which will search for habitable planets
by using visible light with the "signature" of water and/or
oxygen from an Earth-type planet after its scheduled launch
around 2013, and the ESA's
Darwin
project involving six space telescopes
(Astrobiology
Magazine). The stars examined were selected from
a larger list of 17,129 (of which 75 percent are located within around
450 ly, or 140 parsecs, of Sol) that were assembled into a Catalog of
Nearby Habitable Stellar Systems
(HabCat)
by Turnbull and
Jill
Tarter of the SETI
Institute (see:
Margaret C. Turnbull,
2002, in
pdf).
Selection criteria for the 30-star shortlist included:
X-ray luminosity, rotation, spectral types or color, kinematics,
metallicity, and Strömgren photometry. On February 19, 2006,
Turnbull named Chara
as a nearby Sun-like star that is old enough to qualify as the top
candidate for those listening for radio signals from intelligent
civilizations (e.g., the SETI
Institute).

To find life around nearby stars,
the ESA's Darwin mission will look
for traces of water, oxygen, and
carbon dioxide in the atmospheres
of Earth-type planets found in
stellar habitable zones
(more).

Chara

This star is a yellow-orange main sequence dwarf star of spectral and
luminosity type G0 V, with less than 108 percent of Sol's mass, under
111 percent of its diameter, and about 1.2 times its luminosity.
It may be 59 to 120 percent as enriched as Sol with elements heavier
than hydrogen ("metallicity"), based on its abundance of iron
(Cayrel
de Strobel et al, 1991, page 21). Chara's age can be revised
to 4.05 billion years based a new metallicity measurement
indicating 64 percent of Sol's iron abundance and nearly the same
ratio (98 percent) of calcium to iron abundance
(Ibukiyama
and Arimoto, 2002), from a previous estimate of 9.8 billion years
(Ng
and Betelli, 1998). The star was once believed to have an unseen
companion detected through spectroscopic analysis (more below).

The orbit of an Earth-like planet (with liquid water) around the star
would have to be centered around 1.1 AU -- just beyond the orbital
distance of Earth in the Solar System -- with an orbital period around
1.1 Earth years. Chara is a New Suspected Variable star designated
NSV 5725. Useful star catalogue numbers for the star include: Bet
CVn, 8 CVn, HR 4785, Gl 475, Hip 61317, HD 109358, BD+42 2321, SAO
44230, FK5 470, LHS 2579, LTT 13552, and LFT 924.

Constellation Canes Venatici, the Hunting Dogs of the Herdsman Boötes,
was invented by Johannes Hevelius (1611-1687) for his map
of the Constellations in Firmamentum Sobiescianum that was
published posthumously in 1690. For more information about the stars
and objects in this constellation and an illustration, go to Christine
Kronberg's
Canes Venatici.
For another illustration, see David Haworth's
Canes
Venatici.

For more information about stars including spectral and luminosity
class codes, go to ChView's webpage on
The Stars of
the Milky Way.